JPH11352135A - Interatomic force microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interatomic force microscope by which damages on a probe and a sample are reduced by vibrating a cantilever with a frequency below its resonance frequency and by scanning so that contact and separation between the probe and the sample are alternately repeated periodically, and by which interaction acting between the probe and the sample and properties of the sample picturized. SOLUTION: A cantilever or a sample is vibrated vertically relative to the surface of the sample with a frequency below a resonance frequency of the cantilever and scanning is performed so that contact and separation between the probe and the sample are alternately repeated periodically. In this case, the maximum repulsion on the probe is controlled as prescribed, to thereby obtain a topography of the sample. By recording a deflection signal 202 of the scanning cantilever, interaction acting between the probe and the surface of the sample and the distribution of properties of the sample can be picturized. In this device, since the probe and the sample are made to contact periodically, the probe does not drag the sample, to thereby reduce damages to the probe and the sample.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic force microscope for observing a surface shape of a sample by utilizing an atomic force acting between substances.

[0002]

2. Description of the Related Art An atomic force microscope basically includes a cantilever having a probe at its tip and a detector for detecting its deflection, a fine movement mechanism for position control, and controlling them. It consists of a computer for displaying measurement results. Atomic force microscopes are classified into a contact type (contact AFM), a non-contact type (non-contact AFM), and a cyclic contact type according to the scanning method.

[0003] The contact type scans the surface of the sample while the probe is in contact with the surface of the sample.
The distribution of physical properties of the surface such as friction and hardness can be observed. The non-contact method is a method in which a probe is scanned without touching a sample by vibrating a cantilever near its resonance frequency. Since it is non-contact, there is a feature that damage to the sample is small.

The cyclic contact type vibrates the cantilever near its resonance frequency similarly to the non-contact type, but has a difference that the probe periodically scans while contacting the sample. Compared with the contact method, this method has a feature that the sample is less damaged because the drag of the sample is small. The contact type AFM has features not found in the other two methods. It is a measurement of the force acting between the probe and the sample. The measurement of the force is performed by measuring the force curve shown in FIG. This force curve provides important information about the sample surface. In the area 101, information on the unevenness and hardness of the sample surface is obtained, in the area 102, information on the attraction and repulsion acting between the probe and the sample, and in the area 103, information on the attraction force acting between the probe and the sample is obtained.

[0005]

In the conventional force measurement by AFM, usually, after measuring a surface shape image of a sample, a location is designated on the surface shape image, and the force as shown in FIG. This is done by measuring the curve. In this case, what is obtained is information such as the suction force at that position. However, since most sample surfaces are non-uniform, it is necessary to measure the distribution of the attraction force and the like within the surface of the sample surface.

For this purpose, the surface of the sample must be scanned while continuously measuring the force curve. Usually, in order to measure a force curve, a sample or a cantilever is vibrated up and down, and its frequency is at most several tens of Hz.
This is because the vibration is constant speed and the frequency is limited to a low value. Since the surface shape image of a normal AFM is composed of 65536 pixels, even if a force curve is measured at 50 Hz, it takes about 20 minutes to obtain one image. This is about five times the normal AFM measurement.

Therefore, the present invention measures the force curve at high speed,
It is an object to simultaneously measure and image in-plane distribution of information on a sample surface obtained from a force curve such as an adsorption force in addition to a surface shape in a short measurement time equivalent to a normal AFM.

[0008]

In order to solve the above problems, an atomic force microscope of the present invention has a cantilever and a probe, and vibrates a sample or a probe attached to the cantilever with a sine wave. Speeds up the measurement of force curves, and simultaneously measures the in-plane distribution of information about the sample surface obtained from force curves such as adsorption force in addition to the surface shape in a short measurement time equivalent to ordinary AFM. It is one that can be imaged.

Further, by controlling the position of the probe or the sample so as to keep the maximum repulsive force acting on the probe constant, the surface of the sample is manipulated while controlling the atomic force such that a surface shape image of the sample surface can be obtained. The microscope was used. Furthermore, a signal indicating the cantilever deflection when the probe and the sample are sufficiently far apart and the cantilever is not bent, and a signal indicating the cantilever deflection when the probe receives the maximum repulsive force from the sample. The atomic force microscope was designed so that the maximum repulsive force acting on the probe could be determined from the difference from the above.

Further, an atomic force microscope capable of simultaneously imaging a surface shape image of a sample, an interaction acting between the probe and the sample surface on the sample surface, and a physical property distribution of the sample. did. Further, an atomic force microscope capable of imaging attractive and repulsive forces acting between the probe and the sample surface was used.

Further, the timing of two trigger signals synchronized with the vibration of the cantilever or the sample is adjusted, and the attraction and repulsion acting between the probe and the sample are determined from the difference between the signals representing the deflection of the cantilever at each timing. Atomic force microscope that can perform the measurement. Further, an atomic force microscope capable of imaging the distribution of the adsorption force acting between the probe and the sample was used.

Further, the timing of the start and end trigger signals synchronized with the vibration of the cantilever or the sample is adjusted, and the signal representing the deflection of the cantilever between the start trigger and the end trigger is used to perform adsorption between the probe and the sample. The atomic force microscope was such that the force could be determined. Further, an atomic force microscope capable of imaging the distribution of hardness of the sample surface was used.

Furthermore, the timing of two trigger signals synchronized with the vibration of the cantilever or the sample is adjusted, and the hardness of the sample surface can be determined from the difference between the signals representing the deflection of the cantilever at each timing. An atomic force microscope was used. Furthermore, an atomic force microscope was used that can synchronize the timing of acquiring information about the sample surface from the signal representing the deflection of the cantilever with the timing of acquiring information about the surface shape.

Further, an atomic force microscope capable of storing one cycle of a signal representing the deflection of the cantilever at each position on the sample surface or a part thereof in a storage device simultaneously with the measurement of the shape of the sample surface. And Furthermore, the timing for acquiring information on the shape of the sample surface and the timing for storing one cycle or a part of a signal representing the deflection of the cantilever at each position on the sample surface in a storage device are synchronized. An atomic force microscope was developed so as to produce

[0015]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] In the novel AFM described in the present invention, a cantilever or a sample is vibrated at a resonance frequency or lower of the cantilever.

FIG. 2 schematically shows a change in the deflection of the cantilever when the sample is vibrated by a sine wave. The horizontal axis of the graph is time, and the vertical axis is displacement. The curve shown by the solid line is the displacement of the tip of the cantilever, and the broken line is the displacement of the sample. In a state where the probe and the sample are sufficiently separated, no force is applied to the probe, so that the position of the tip of the cantilever does not change. As the sample approaches the probe, an attractive force acts between the probe and the sample, and at a point a where the gradient of the attractive force and the spring constant of the cantilever are balanced, the cantilever bends toward the sample side and the probe comes into contact with the sample surface. Thereafter, the probe rises with the sample and the cantilever flexes upward. After the maximum displacement of the sample, the probe descends with the sample and the cantilever flexes downward. In many cases, the probe lowers further than the position at point a due to the attraction force. The probe moves away from the sample surface at point d where the adsorption force and the restoring force of the cantilever balance,
The cantilever starts free vibration. In the atmosphere, the free vibration is attenuated by the viscous drag of the atmosphere, the cantilever returns to a non-deflected state, and the probe again contacts the sample at point e. From the amount of deflection of the cantilever from point a to point e, information on the interaction between the probe and the sample and the physical properties of the sample surface can be obtained. For example, in the region from the point a to the point d where the probe is in contact with the sample, information on the hardness of the sample surface can be obtained.

Further, information on the adsorption force acting between the probe and the sample can be obtained from the amount of deflection of the cantilever at the point d where the probe is separated from the sample surface, and from the amount of deflection of the cantilever immediately before the point e, Information on the attraction and repulsion acting between the probe and the sample can be obtained. Further, while performing feedback control so as to keep the maximum amount of deflection 201 of the cantilever when the probe is pushed up by the sample, by scanning the sample surface, in addition to the surface shape of the sample, the probe and the sample It is possible to obtain a distribution image of the interaction between the particles and the physical properties of the sample surface.

[Embodiment 2] In the AFM, the deflection of the cantilever is detected by a deflection detector. The deflection detector outputs an electric signal (deflection signal) proportional to the deflection of the cantilever. 3 and 4, a deflection signal processing apparatus for acquiring information on the surface shape of the sample, the interaction between the probe and the sample, and the physical properties of the sample surface described in the first embodiment from the deflection signal. Will be described. 3 and 4 are a block diagram of the deflection signal processing device and a timing chart showing the operation of the deflection signal processing device, respectively.

The deflection signal processing device mainly includes a trigger generation circuit 301 for generating a trigger synchronized with an excitation signal for vibrating the cantilever or the sample, trigger adjustment circuits 303a to h for adjusting trigger timing, a reference signal sample and hold circuit. 304, local maximum hold circuit 305, local minimum hold circuit 306, sample and hold circuit 307 for attractive and repulsive forces, sample and hold circuits 308 and 30 for elasticity
9. It is composed of subtractors 310a to 310d.

The deflection signal from the deflection detector is a reference signal sample & hold circuit 304, a maximum value hold circuit 305, a minimum value hold circuit 306, a sample & hold circuit for attractive / repulsive force 307, a sample & hold circuit for elasticity 3.
Input to 08 and 309. By using the trigger adjustment circuit 303a to adjust the trigger timing to the state in which the cantilever is not bent as shown at 402a, the reference signal sample & hold circuit 304 can be used in a state where the cantilever serving as the reference signal is not bent. Output the magnitude of the deflection signal. This reference signal indicates a state in which the cantilever does not bend.

The local maximum hold circuit 305 is a circuit for detecting and outputting a local maximum within an arbitrary time window. The timings of 403b and 403c are adjusted using trigger adjustment circuits 303b and 303c. At this time, the time when the deflection signal 401 becomes maximum is set between 403b and 403c. The maximum value hold circuit 305 detects and outputs the maximum value of the deflection signal 401 within the time from the trigger 403b to the trigger 403c. By scanning the sample surface while performing feedback control so as to keep the difference between this signal and the reference signal constant, the surface shape of the sample can be obtained.

The minimum value hold circuit 306 is a circuit that detects and outputs a minimum value within an arbitrary time window. The timings of 404d and 404e are adjusted using trigger adjustment circuits 303d and 303e. At this time, the time at which the probe separates from the sample is adjusted so as to fall between 404d and 404e. The minimum value hold circuit 306 detects and outputs the minimum value of the deflection signal 401 within the time from the trigger 404d to the trigger 404e. The difference between this signal and the reference signal indicates the magnitude of the adsorption force acting between the probe and the sample. If the spring constant of the cantilever is used, the attraction force can be obtained.

Sample / hold circuit 307 for attractive / repulsive force
However, the timing of sampling the flexure signal is determined by using the trigger adjustment circuit, 303f, and as shown in 405f, the cantilever bends due to the attractive or repulsive force acting between the probe and the sample immediately before the probe contacts the sample. Adjust to the area where you are. Attraction / repulsion sample & hold circuit 30
The difference between the output of 7 and the reference signal indicates the magnitude of the interaction between the probe and the sample, such as the attractive and repulsive forces acting between the probe and the sample.

Sample and hold circuits 308 and 3 for elasticity
The timing at which 09 samples the deflection signal is determined by using trigger adjustment circuits 303g and 303h,
As shown in h, the probe is in contact with the sample, and the time is adjusted on either side where the deflection of the cantilever increases or decreases. The difference between the outputs of the elastic sample and hold circuits 308 and 309 indicates the hardness of the sample surface.

While scanning the surface of the sample, a signal reflecting the surface shape, the attractive force, the attractive force / repulsive force, and the hardness is sampled, and the distribution of the attractive force, the attractive force / repulsive force, and the hardness simultaneously with the surface shape image. An image can be obtained. In addition, by synchronizing the signal for oscillating the sample or the cantilever with the sampling timing for acquiring the surface shape image and the like, the consistency between the actual sample surface and the acquired image can be further improved.

[Embodiment 3] FIGS. 5 and 6 are a block diagram and a timing chart of a deflection signal processing device. The deflection signal processing device mainly includes a trigger generation circuit 501 for generating a trigger synchronized with an excitation signal for vibrating the cantilever or the sample, trigger adjustment circuits 503a to 503e for adjusting trigger timing, sampling circuits and storage devices 504 and 509, It comprises a reference signal sample & hold circuit 505, a local maximum value hold circuit 506, and a subtractor 507.

The deflection signal from the deflection detector is input to a sampling circuit and storage device 504, a reference signal sample and hold circuit 505, and a local maximum hold circuit 506. By using the trigger adjustment circuit 503a to adjust the trigger timing to a state where the cantilever is not bent as shown in a of 602, the reference signal sample & hold circuit 505 can be used in a state where the cantilever serving as the reference signal is not bent. The magnitude of the deflection signal is output. This reference signal indicates a state in which the cantilever does not bend.

The local maximum hold circuit 506 is a circuit that detects and outputs a local maximum within an arbitrary time window. The timings of 603b and 603c are adjusted using trigger adjustment circuits 503b and 503c. At this time, the time when the deflection signal 601 becomes maximum is set between 603b and 603c. The maximum value hold circuit 506 detects and outputs the maximum value of the deflection signal 601 within the time from the trigger 603b to the trigger 603c. By scanning the sample surface while performing feedback control so as to keep the difference between this signal and the reference signal constant, the surface shape of the sample can be obtained.

The sampling circuit and the storage device 504 include:
From time 602a to time 602d, the deflection signal is sampled and one cycle of the deflection signal at each point on the sample surface is continuously stored in the storage device. After measuring the surface shape image, an attraction / repulsion distribution image, an attraction force distribution image, and a hardness distribution image are formed by extracting a deflection signal at an arbitrary timing from the deflection signal stored in the storage device.

The sampling circuit and the storage device 50
Numeral 9 is for sampling a part of the deflection signal and storing it in a storage device. The sampling range is
Using trigger adjustment circuits 503d and 503e, 604e and 604f
Adjust as shown. Here, 604e and 604f are a start trigger and an end trigger of sampling, respectively. By using multiple similar circuits, multiple arbitrary portions of the flex signal can be sampled and stored in a storage device. Thereby, the capacity of the storage device can be reduced.

As described above, by recording and storing all or a part of the flexure signal, it is possible to obtain not only the in-plane distribution but also the distribution of the interaction between the probe and the sample with respect to the distance between the probe and the sample. In addition, by synchronizing a signal for oscillating the sample or the cantilever and a sampling timing for acquiring a surface shape image and the like and a timing at which the sampling circuit and the storage device start sampling, the actual sample surface and the acquired image are obtained. Can be further improved.

[Fourth Embodiment] FIGS. 7 to 9 are block diagrams of an AFM using the third to fourth embodiments. FIG.
FIG. 2 is a block diagram of an AFM in which a sample is vibrated using an XYZ translator 705 for scanning a sample. The sample is vibrated by superimposing the excitation signal on the height control signal on the Z terminal of the XYZ translator 705 using the adder 711.

Although the method of vibrating the sample using the XYZ translator of FIG. 7 is simple, it is generally used.
Since the resonance frequency of the XYZ translator is low, the range of the excitation frequency is narrowed. Therefore, as shown in FIG.
By adding a vibration actuator 810 having a high resonance frequency independently of the XYZ translator and vibrating the sample, the range of the vibration frequency can be widened.

As shown in FIG. 9, the same effect can be obtained by fixing the cantilever to the vibration actuator 910 and vibrating the cantilever.

[0035]

According to the conventional AFM, the probe-sample interaction measurement, which was limited to measurement at a single point on the sample surface, is now improved by the present invention in addition to the interaction distribution in the plane and the sample surface. Measurement of the interaction distribution in the vertical direction. Further, as a secondary effect, the number of times that the probe contacts the sample is smaller than that of the cyclic contact type, so that the sample and the probe are less damaged.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a force curve with respect to distance. A portion surrounded by a circle or an ellipse indicates an area where each piece of information can be obtained.

FIG. 2 is a diagram illustrating a deflection curve with respect to time showing a change in deflection of a cantilever when a sample is vibrated as an example of an AFM to which the present invention is applied.

FIG. 3 is a block diagram of a deflection signal processing device.

FIG. 4 is a timing chart showing the operation of the device according to the present invention.

FIG. 5 is a block diagram of another type of deflection signal processing device.

FIG. 6 is a timing chart showing the operation of another type of apparatus according to the present invention.

FIG. 7 is a block diagram of an AFM to which a sample is scanned and which is excited by a Z translator of an XYZ translator to which the present invention is applied.

FIG. 8 is a block diagram of an AFM of a type to which the present invention is applied, in which a sample is scanned and vibrated by an actuator added to an XYZ translator.

FIG. 9 is an application of the present invention, in which a sample is scanned, and a cantilever is fixed to an actuator to vibrate the AFM.
It is a block diagram of.

[Explanation of symbols]

101 Topography of the sample from the force curve against distance,
The area where information on viscoelasticity is obtained 102 The area where information on the attractive and repulsive forces between the probe and the sample is obtained from the force curve for the distance 103 The information on the adsorption force acting between the probe and the sample is obtained from the force curve on the distance 103 Area 201 Signal used for feedback control and topography image 202 Deflection signal of cantilever 204 Signal indicating magnitude of adsorption force acting between probe and sample 205 Signal indicating hardness of sample surface 206 Probe and sample Signal indicating the magnitude of the attractive / repulsive force acting between 310 Subtractor 311 Computer and AFM controller 401 Flexure signal of cantilever 402 Trigger signal for reference signal acquisition 403 Trigger signal for maximum value hold circuit 404 Trigger signal for minimum value hold circuit Trigger signal 405 Trigger for sample and hold circuit for attractive / repulsive force Signal 406 Trigger signal for sample and hold circuit for elasticity 407 Trigger signal for sample and hold circuit for elasticity 507 Subtractor 508 Computer and AFM controller 602 Trigger signal for maximum value hold circuit 603 Trigger signal for acquiring reference signal 604 Sampling Trigger signal specifying range 703 Cantilever 704 Sample 705 XYZ translator 706 Flexure signal processor 707 Computer and AFM controller 708 Oscillator 709 Z translator controller 710 XY translator controller 711 Adder 808 Oscillator 810 Piezoelectric actuator for excitation 908 Oscillator 910 Excitation Piezo actuator

Continued on the front page (72) Inventor Toshihiko Sakuhara 1-8-8 Nakase, Mihama-ku, Chiba City, Chiba Prefecture Inside Seiko Instruments Inc. (72) Inventor Tatsuaki Ataka 1-8-1, Nakase, Mihama-ku, Chiba City, Chiba Instruments Corporation (72) Inventor Masamichi Fujihira 1103-5 Shimo Aso, Aso-ku, Kawasaki City, Kanagawa Prefecture Masamichi Fujihira

Claims (20)

[Claims] An atomic force microscope having a cantilever and a probe, and collecting data reflecting the sample surface with respect to the position of the probe when the tip of the probe attached to the cantilever scans the surface of the sample. In, the probe or the sample is vibrated at a frequency equal to or lower than the resonance frequency of the cantilever, by scanning the sample surface while periodically contacting the probe and the sample, in addition to information on the shape of the sample surface An atomic force microscope, wherein a plurality of pieces of information representing the properties of the sample surface are obtained and imaged simultaneously. 2. In the atomic force microscope, a surface shape image of the sample surface is obtained by operating the sample surface while controlling the position of the probe or the sample so as to keep the maximum repulsive force acting on the probe constant. The atomic force microscope according to claim 1, wherein: 3. A signal representing the deflection of the cantilever when the distance between the probe and the sample is sufficiently large and the cantilever is not bent, and the deflection of the cantilever when the repulsive force received by the probe from the sample is maximum. 3. The atomic force microscope according to claim 2, wherein a maximum repulsive force acting on the probe is determined from a difference from a signal representing the force. 4. Adjusting the timing of a trigger signal synchronized with the vibration of a cantilever or a sample, and measuring a signal representing the deflection of the cantilever in accordance with the trigger to reduce the deflection of the cantilever when the cantilever is not bent. 4. An atomic force microscope according to claim 3, wherein a signal to be represented is determined. 5. The timing of a start and end trigger signal synchronized with the vibration of the cantilever or the sample is adjusted, and the maximum repulsive force acting on the probe is determined from a signal representing the deflection of the cantilever between the start trigger and the end trigger. The atomic force microscope according to claim 3, wherein: 6. The method according to claim 1, wherein after the probe contacts the sample surface, the probe is vibrated with an amplitude large enough to separate the probe from the sample surface.
Atomic force microscope as described. 7. The atomic force microscope according to claim 1, wherein the oscillating step oscillates with a sine wave. 8. The method according to claim 1, wherein a surface shape image of the sample, an interaction between the probe and the sample surface on the sample surface, and a physical property distribution of the sample are simultaneously imaged. Atomic force microscope. 9. The atomic force microscope according to claim 8, wherein attraction and repulsion acting between the probe and the sample surface are imaged. 10. The timing of two trigger signals synchronized with the vibration of the cantilever or the sample is adjusted, and the attraction and repulsion acting between the probe and the sample are determined from the difference between the signals representing the deflection of the cantilever at each timing. The atomic force microscope according to claim 9, wherein: 11. The atomic force microscope according to claim 8, wherein the distribution of the attraction force acting between the probe and the sample is imaged. 12. A method of adjusting the timing of a start and end trigger signal synchronized with the vibration of a cantilever or a sample, and performing adsorption between the probe and the sample based on a signal representing the deflection of the cantilever between the start trigger and the end trigger. The atomic force microscope according to claim 11, wherein the force is determined. 13. The atomic force microscope according to claim 8, wherein a distribution of hardness of the sample surface is imaged. 14. The method according to claim 1, wherein the timing of the two trigger signals synchronized with the vibration of the cantilever or the sample is adjusted, and the hardness of the sample surface is determined from the difference between the signals representing the deflection of the cantilever at each timing. An atomic force microscope according to claim 13. 15. The apparatus according to claim 10, wherein the timing of acquiring information on the surface of the sample from the signal representing the deflection of the cantilever and the timing of acquiring information on the surface shape are synchronized.
Atomic force microscope according to any one of the above. 16. The apparatus according to claim 2, wherein one cycle of a signal representing the deflection of the cantilever at each position on the sample surface or a part thereof is stored in the storage device simultaneously with the shape measurement of the sample surface. Atomic force microscope. 17. The apparatus according to claim 15, wherein a timing for acquiring information on the shape of the sample surface and one cycle of a signal representing the deflection of the cantilever at each position on the sample surface or a part thereof are stored. 3. The atomic force microscope according to claim 2, wherein the timing of storing the information in the apparatus is synchronized. 18. The method according to claim 1, wherein the attraction and repulsion acting between the probe and the sample are determined from a signal representing the deflection of the cantilever for one cycle stored in the storage device, and the distribution of the attraction and repulsion is imaged. The atomic force microscope according to claim 16 or 17, wherein: 19. The method according to claim 19, wherein a suction force acting between the probe and the sample is determined from a signal representing the deflection of the cantilever for one cycle stored in the storage device, and the distribution of the suction force is imaged. Item 18. An atomic force microscope according to item 16 or 17. 20. The method according to claim 16, wherein the hardness of the sample is determined from a signal representing the deflection of the cantilever for one cycle stored in the storage device, and the hardness distribution is imaged.
Or the atomic force microscope according to 17.